Synthetic routes to heterocycloheptatrienes will be devised. Heteroatoms will include silicon, germanium, tin, boron, phosphorous, selenium and tellurium. These systems are inherently interesting from the viewpoint of electronic structure, thermal and photochemical behavior and as theoretical models. The question of possible aromaticity will be examined in detail. As almost no examples of any of these ring systems are now known, they will be submitted for chemotherapeutic value testing. A number of nitrogen analogs have been found to be valuable medicinal agents. A unifying feature of this study will be the influence of a heteroatom upon the ground-state and excited-state properties of this basic ring system. The present lack of information in this area can be attributed to a scarcity of synthetic approaches. A number of pathways are presented in the body of this proposal to alleviate this difficulty. BIBLIOGRAPHIC REFERENCES: "The Photochemistry of 2-Phenylselenophene and 2-Phenyltellurophene," T.J. Barton, C.R. Tully and R.W. Roth, J. Organometal. Chem., 108, 183 (1976). "An Alternative Mechanism for the Formation of 1,4-Disilacyclohexa-2,5-dienes from Acetylenes and Silylenes," T.J. Barton and J.A. Kilgour, in press. J. Amer. Chem. Soc.